JP3027800B2 - Transmission control method and transmission control device in wireless LAN - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission control method and a transmission control device, and more particularly to a transmission control method and a transmission control device in a wireless LAN in which transmission efficiency does not decrease even if an error rate increases due to noise or the like.

[0002]

2. Description of the Related Art In recent years, various wireless LANs (local area networks) have been proposed. FIG. 6 is a block diagram showing a configuration example of a conventional wireless LAN system. Well-known CSMA
/ CD or CSMA / CA LAN 71
The server 70 or various terminals and printers (not shown) are connected, and a transmission control device 72 for wireless LAN is also connected. For example, a personal computer PC 78 is connected to the transmission control device 75 as a terminal device.

The transmission control devices 72 and 75 are LAN
Controllers 73 and 77 and modulation / demodulation / transmission / reception circuit 7
4 and 76, and the LAN controller 73 is LA
The LAN packet received from N71 is output to the modulation / demodulation / transmission / reception circuit 74, and the modulation / demodulation / transmission / reception circuit 74 modulates and transmits the received LAN packet as it is. Then, the packet received by the modulation / demodulation / transmission / reception circuit 76 has been directly transmitted to the terminal PC 78 via the LAN controller 77.

[0004]

In the conventional LAN as described above, the LAN transmitted through the LAN 71 is used.
Packets are transmitted in large blocks, for example, up to about 1500 bytes. Then, the wireless LA as shown in FIG.
In the N system, when the server 70 communicates with the PC 78, error retransmission control is performed between the server and the PC. Therefore, when the conventional LAN packet is applied to the wireless LAN as it is, when the bit error rate in the wireless transmission section increases, the transmission efficiency decreases due to retransmission control and transmission delay in the wireless section. there were.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a transmission control method and a transmission control apparatus in a wireless LAN in which the transmission efficiency does not decrease even if the error rate increases due to noise or the like. It is in.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a wireless LAN.
Is characterized by a transmission control method or a transmission control apparatus in which data divided into blocks is further divided into cells, an error detection code is added to each cell, and a plurality of cells are packet-transmitted in blocks. When an error is detected in units of cells, retransmission control is performed in units of cells.

In general, when data is packetized and transmitted, as the error rate of the transmission path is smaller, the use of longer packets improves the transmission efficiency. On the other hand, when the error rate is higher, frequent retransmission processing is performed. Occurs and the transmission efficiency decreases. Also, in the case of packetization, as the packet length is longer, the ratio of extra data other than the data to be transmitted, such as a header and an error detection code, is reduced, and the transmission efficiency is improved. Also, when the packet length is shortened, the ratio of excess data increases, and the transmission efficiency decreases.

A wireless LAN is more susceptible to external noise than a wired LAN, and the S / N ratio is reduced due to obstacles or the like, so that the bit error rate may vary greatly. In such a case, if the present invention is applied, by making the size of a cell which is an error detection and retransmission unit smaller than the size of a packet (block) which is a transmission unit, even when retransmission increases, retransmission control can be performed. By making the transmission unit (packet) in normal operation larger than the retransmission unit, the transmission efficiency in normal transmission without retransmission can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows a wireless LAN to which the present invention is applied.
It is a block diagram showing an example of a system. A server 1 having a shared storage device 2, a plurality of personal computers PCs 6, 7, and a router 4 are connected by a LAN 3, and the router 4 is connected to an RHUB 6 which is a communication control device to which the present invention is applied. Note that the router 4 is an apparatus that outputs only a packet having a predetermined address set in advance to the RHUB 5 among the packets on the LAN 3.

RHUB5 is a radio communication control device,
Details will be described later. 10Base-T for RHUB8,9
A plurality of PCs 10, 11, 12 and 13 are connected via a LAN interface such as.
The access control in the wireless section between the RHUBs employs, for example, the well-known CSMA / CA method. At the time of transmission, the wireless channel is checked for vacancies, and different pattern data is transmitted for each RHUB. Is detected. Then, data transmission is started only when there is no collision.

FIG. 2 is a block diagram showing the configuration of the RHUB. The LAN controller LANC 20 has a built-in CPU and accommodates a LAN terminal 23 for connecting to the router 4 or the LAN 3 in FIG. Then, for example, transmission control in a well-known CSMA / CD system LAN is executed. The buffer 22 is used for temporarily storing transmitted and received LAN packets. The HUB 21 has a plurality of LAN terminals 24 to 2 of 10BASE-T standard, for example.
5 is a well-known circuit for configuring a star LAN, and is also connected to a LAN controller 20. The HUB 21 includes, for example, a plurality of PCs 10-1 in FIG.
3 are connected.

The CPU 26 is a processing device for controlling the entire RHUB. The CPU 26 is connected to the bus 32 and has a parallel port for connecting to the gate array GA30. The ROM 27 stores an RHUB control program, and the RAM 28 is used as a buffer and a work area. The panel circuit 29 is, for example, a DIP
It is composed of switches and LED lamps, and inputs various parameters or displays the status of the device. When a system is installed, an interface circuit such as RS232C may be provided to externally set many parameters, or an EEPROM may be provided for storing various parameters.

The gate array GA30 is a circuit for scrambling packet data in units of cells, which will be described later, and adding an ECC (error check code) in units of cells. Although any scrambling method can be adopted, it is necessary to perform high-speed processing.
For example, data is processed by combining data shift, bit replacement, bit arrangement inversion, and the like. The above processing is executed by a hardware circuit combining a shift register and a gate circuit in a gate array.

The transmission / reception circuit TRX31 includes a data modulation / demodulation circuit, a transmission circuit, and a reception circuit.
In z, wireless data transmission is performed at a transmission rate of 1 Mbps. As a modulation method, any method such as FSK, PSK, and QAM can be adopted, and a direct spread method or a frequency spread method based on a frequency hopping method may be adopted.

FIG. 3 is a functional block diagram showing the function of the RHUB, and FIG. 4 is an explanatory diagram showing a procedure for generating a transmission packet from a LAN packet. Hereinafter, the function will be described with reference to FIGS. In FIG. 3, the upper part represents the transmission function, and the lower part represents the reception function. Blocking unit 4
0 divides the LAN packet 50 output from the LAN controller 20 as data to be transmitted into blocks 51 to 52 each having a predetermined length (for example, 256 bytes) or less.

The reason for the division is that, for example, a packet transferred in the LAN 3 of FIG. 1 has a maximum of 1500 bytes, which is too large to reduce the transmission efficiency in a wireless section. Further, dummy data is added to the last block so that the length of each block is an integral multiple of the length of the cell 53 that is a predetermined length.

The transmission control (retransmission) unit 41 takes out each of the divided blocks one by one and generates a packet header 55 including a destination address, a source address, a serial number, and the like. Then, the data part, that is, the block of the transmission packet is scrambled and output to the ECC adding unit 42. Also, the access control of the wireless channel is performed, and the wireless channel is monitored, and when it is confirmed that the wireless channel is free, the transmission process is started. The processes of the blocking unit 40 and the transmission control unit 41 are executed by the CPU 26.

The scramble and ECC adding section 42 receives the data portion of the packet, generates data 53 by dividing the data into predetermined lengths (for example, 64 bytes), and scrambles the data in units of cells according to the method described above. multiply. After that, the error check code EC is further added in cell units.
C is generated and added to the cell 53. Then, the processed cell 54 is modulated and output to the transmitting unit 43. As the ECC method, any known method such as parity can be adopted. This process is executed by the GA 30. modulation,
The transmission unit 43 scrambles the data part,
For example, the packet data to which the ECC has been added is subjected to, for example, FSK modulation, frequency conversion to a transmission frequency, frequency spread processing, and transmission from the antenna.

The receiving / demodulating unit 44 receives, demodulates, and outputs the packet data. The ECC extraction and descrambling unit 45 decomposes the data portion of the received packet into cells, extracts ECC for each cell, and checks for errors. Also,
The descrambling process is performed based on a predetermined decoding parameter, and the original data is output.

The transmission control (error detection) unit 46 receives the error check result and the restored data from the ECC extraction and descrambling unit 45, and if there is no error, outputs the data as it is to the packet decomposing unit 47. If detected, the cell data is discarded, and an instruction is issued to transmit a retransmission request packet for the cell. When all the cells of the received packet are received normally, the packet decomposing unit 47 decomposes the received packet to extract data, and restores the original LAN packet 50.

FIG. 5 is an explanatory diagram showing a cell retransmission procedure. In this example, an example in which four cells are transmitted by one packet is disclosed. The header of the transmission packet includes a serial number, and each cell is assigned serial numbers 0 to 3 in the packet. First, the transmitting-side RHUB transmits the (k-1) -th packet 60. When the receiving-side RHUB receives the packet 60 normally, it returns an acknowledgment ACK packet 61. As described above, since ACK is returned in packet units at the time of normal reception, transmission efficiency at normal time is improved as compared with transmission in cell units.

When noise is mixed in when the transmitting RHUB transmits the k-th packet 62 and an error occurs in the second cell, the error is detected by the receiving RHUB, and the receiving RHUB transmits the k-th packet 62. A negative acknowledgment NAK packet 63 requesting retransmission of the second cell of the second packet is returned. Upon receiving the NAK packet 63, the transmitting RHUB extracts data corresponding to the second cell of the k-th packet to be retransmitted, scrambles and adds ECC, generates a retransmitted packet header, and generates the second cell. Is retransmitted by the retransmission packet 64.

As described above, only cells having errors are retransmitted at the time of retransmission, so that transmission efficiency is improved at the time of retransmission control as compared with the retransmission method in a packet unit. If an error is detected in a plurality of cells, the NAK packet 63
Request for retransmission of a plurality of cells, and a retransmission packet 64
To retransmit multiple cells.

The retransmission packet 64 at the receiving RHUB
Is normally received, the receiving RHUB returns an acknowledgment ACK packet 65 indicating that the second cell of the k-th packet has been normally received, and the transmitting RHUB returns k +
The first packet 66 is transmitted. Note that instead of confirming an ACK for each packet, a selective-repeat ARQ that transmits a plurality of packets without waiting for an ACK
A method may be adopted. Since the transmission control is performed according to the above-described procedure, it is possible to construct a system in which the transmission efficiency does not decrease even if the error rate of the transmission path fluctuates significantly during communication.

Although the embodiments have been disclosed above, the following modified examples are also conceivable. The block length and the cell length may be determined based on the error rate of the transmission path and its fluctuation range so as to maximize the transmission efficiency. In the present invention, the block length is increased even when the error rate is large. It is possible. The cell length is longer when the error rate is small and shorter when the error rate is large, so that the transmission efficiency is improved. For example, in each RHUB, the error rate of the transmission path is constantly monitored for each RHUB of the communication partner. Then, the cell length is set to, for example, 16 bytes, 32 bytes, 64 bytes based on the error rate.
You may make it select from bytes.

In the embodiment, the EC is independently set for each cell.
C, but the header is also independently ECC
May be added, and when an error is detected, the packet may be discarded. In the embodiment, scrambling is performed for each cell. However, when the transmission control method of the present invention is performed, whether or not scrambling is performed is arbitrary.

In the embodiment, the configuration is described in which the transmission packet is always scrambled and ECC-attached and output to the transmission unit. The information may be stored in a buffer, and when retransmission is necessary, a necessary cell may be extracted from the buffer and transmitted. Furthermore, if the processing capability of the CPU is sufficient, scrambling and ECC addition can be processed by software.

In the embodiment, an example in which the access control in the radio section is based on the CSMA / CA system is disclosed. In this system, when one RHUB starts transmission, the other RHUB waits until the transmission ends. There must be. Therefore, a specific RHUB 5 performs TDMA control as a master station, provides a plurality of time slots, and allocates an empty slot from among the plurality of time slots to the RHUB of the slave station that has requested transmission. Is also good. Further, an access control method such as FDMA or CDMA may be employed.

[0029]

As described above, according to the present invention,
Particularly, in a transmission path such as a wireless LAN which is susceptible to external noise and in which the bit error rate fluctuates, the size of a cell as a unit of error detection and retransmission is determined by the size of a packet (block) as a transmission unit. By making it smaller, the transmission efficiency at the time of retransmission control is improved,
By making the transmission unit (packet) in the normal state larger than the retransmission unit, there is an effect that the transmission efficiency in the normal transmission can be improved. Therefore, even if the error rate of the transmission path fluctuates significantly during communication, it is possible to construct a system in which the transmission efficiency does not decrease.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a wireless LAN system to which the present invention is applied.

FIG. 2 is a block diagram illustrating a configuration of an RHUB.

FIG. 3 is a functional block diagram showing functions of RHUB.

FIG. 4 is an explanatory diagram showing a procedure for generating a transmission packet from a LAN packet.

FIG. 5 is an explanatory diagram showing a cell retransmission procedure.

FIG. 6 is a block diagram showing a conventional wireless LAN system.

[Explanation of symbols]

1 ... Server, 2 ... DB, 3 ... LAN, 4 ... Router, 5,
8, 9 ... RHUB, 6, 7, 10, 11, 12, 13 ...
PC, 20 LANC, 21 HUB, 22 buffer, 23, 24, 25 LAN connection terminal, 26 CP
U, 27 ROM, 28 RAM, 29 panel, 30
... GA, 31 ... TRX, 32 ... Antenna

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-247132 (JP, A) JP-A-8-154096 (JP, A) JP-A-7-336368 (JP, A) 318930 (JP, A) JP-A-6-77963 (JP, A) JP-A-3-22646 (JP, A) JP-A-2-186733 (JP, A) JP-A-2-155335 (JP, A) JP-A-55-120249 (JP, A) IEICE Technical Report Vol. 95 No. 532, IN95-103, Takayuki Nakao et al., "Performance Evaluation on Error Control when Accommodating Wireless Terminals in ATM Networks," pages. 29-34 Information Processing Society of Japan, Vol. 98, No. 33, 98-OS-78, 1998.5.7, Yosuke Tamura et al., "Proposal and Implementation of TCP Retransmission Method in Wireless LAN Environment," pages. 71-77 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04L 12/28 H04B 7/26 H04L 1/16 JICST file (JOIS) INSPEC (DIALOG) WPI (DIALOG)

Claims (2)

(57) [Claims] 1. A transmission control method in a wireless LAN which is connected to a wired LAN, converts data into wireless packets and wirelessly transmits the data, a first step of dividing a LAN packet received from the wired LAN into blocks having a predetermined length or less; A second step of adding dummy data after the data of the last block so that the data length of the data of the last block divided by the block generating means is an integral multiple of the cell length that is a predetermined length; A third step of further dividing the block data into cell units of a predetermined length shorter than the block and adding an error detection code for each cell; and concatenating a plurality of cells generated by the cell generation unit in the block unit And a fourth step of generating a wireless packet by adding a wireless packet header and wirelessly transmitting the wireless packet. Sixth extracting Kudeta, detecting a fifth step of dividing the block data to the cell, the error of the cells output from the cell extraction means
And a seventh step of retransmitting a cell for which an error has been detected by the error detection means to the partner apparatus, and an eighth step of retransmitting only the cell requested to be retransmitted by the partner apparatus. A transmission control method in a wireless LAN. 2. A transmission control device for a wireless LAN connected to a wired LAN and configured to wirelessly transmit data by packetizing data, comprising: a block generating means for dividing a LAN packet received from the wired LAN into blocks of a predetermined length or less; Dummy data adding means for adding dummy data after the data of the last block so that the data length of the data of the last block separated by the generating means is an integral multiple of the cell length which is a predetermined length; The block data is further divided into cell units of a predetermined length shorter than the block, and a cell generation unit that adds an error detection code for each cell, and a plurality of cells generated by the cell generation unit are connected in units of the block, A block transmission means for generating a wireless packet by adding a wireless packet header and wirelessly transmitting the packet; A cell extracting means for receiving a packet to extract block data, dividing the block data into cells, an error detecting means for detecting an error of a cell output from the cell extracting means, and detecting an error by the error detecting means. A transmission control apparatus in a wireless LAN, comprising: retransmission request means for requesting a retransmission of a cell which has been retransmitted to a partner apparatus; and retransmission control means for retransmitting only the cell requested to be retransmitted by the partner apparatus.